Dissolving of polymers



Patented July 23, 1946 mssoLvns G F POLYMERS Ray Clyde Houtz, Snyder, N.Y., assignor to E. I. du Pont deNemours & Company, Wilmington. Del., acorporation of Delaware No Drawing. Application December 14, 1944,Serial No. 568,194

Y 9 Claims. 1

This invention relates to a new composition of matter and shapedarticles produced therefrom.

' More particularly, this invention relates to an organic solventsolution of polyacrylonitrile, i. e. polymerized acrylonitrile orpolymerized vinyl cyanide (CHz=CHCN), and copolymers and interpolymersof acrylonitrile in which at least 85% by weight of the polymerisacrylonitrile, and to the production of shaped articles from saidorganic solvent solution of said polymers of acrylonitrile,

Polyacrylonitrile, and copolymers and interpolymers of acrylonitrilewith other polymerizable substances, for example vinyl or acryliccompounds, in which at least 85% by weight of the polymer isacrylonitrile have been known for some time and recognized as possessingdesirable physical and chemical properties including toughness andinsolubility in and insensitivity. to common organic solvents such asmethyl or ethyl alcohol, acetone, ethyl ether, ethyl acetate,hydrocarbon solvents, chlorinated hydrocarbons and the like. Because ofthese facts, numerous attempts have been made to form these polymericmaterials into yarns, films and other shaped articles.

The copending application of George H. La-

. 2 the resulting compositions. in such a manner. Their extrusion intocoagulating baths of the type proposed (including such non-solvents foracrylonitrile as water, dilute acid, dilute salt solutions, etc.) resultin the formation of shaped articles that contain large amounts of theinorganic salt of the proposed solvent. These salts are distributedthroughout the structure and tham, Serial No. 562,012, flied Nov. 4,1944, dis-fcloses solutions of polyacrylonitrile in dimethyl, carbamylcompounds and the production of extruded and otherwise shaped articlesand structures from such solutions. The above-said application of GeorgeH. Latham represents the first successful dissolution ofpolyacrylonitrile in a solvent to produce a solution which is suitablefor the production of commercially useful textile yarns or wrappingtissue films and similar tough, flexible structures. 1

The present application relates to a similarly satisfactory dissolutionof polyacrylonitrile in an organic solvent taken from a different classof organic compounds and the polyacrylonitrile solutions producedthereby are similarly satisfactory for the production of tough,fiexibla'dense, colorless yarns and films which are suitable for use inpractically all general commercial applications of such products.

It has been known heretofore that concentrated aqueous solutions ofinorganic salts such.

destroy the continuity, of the polyacrylonitrile phase and the structurepossesses poor physical properties. Removal of these salts, whenpossible, results in the formation of a porous, spongy, weak,undesirable structure that is very brittle and completely unsuited foruse as a yarn or film. Moreover, when it is attempted to' form amultifilament yarn by extruding, for example the proposed aqueous sodiumsulfocyanide polyacrylonitrile composition, into a dilute acid bath,

it is found that the individual filaments obtained stick together toform an essentially monofilament structure that is extremely brittle andcannot be bent or worked without breaking.

U. S. Patent 1 {o. 2,167,537 to Tobis points out that certain cop lymersof acrylonitrile and an acrylic acid ester (those copolymers containingnot more than of acrylonitrile) are soluble in mixtures of organicsolvents such as dioxan, monochlorbenzene, cyclohexanone, etc. However,these liquids are incapable of dissolving or even swellingpolyacrylonitrile or copolymers of acrylonitrile containing higherpercentages of acrylonitrile, i. e. acrylonitrile polymers of thetypewith which this invention is concerned. As previously mentioned,polymers containing such high percentages (at least by weight) ofacrylonitrile are especially desirable for use because of their gOOdphysical properties and excellent chemical resistance.

It has also been proposed (Rein U. S. Patent No. 2,117,210) to dissolvepolyacrylonitrile in molten quaternary ammonium salts such as benzylpyridinium chloride, an ionizable salt. Although the resulting solutioncan allegedly be used to form yarns or films of polyacrylonitrile, thesolution itself is dark red to brown in color, indicating that somedecomposition of the polyacrylonitrile or some reaction between thepolyacrylonitrile and the molten salt has probably taken place. Suchsolutions are not satisfactory for the production of commerciallyuseful, shaped articles of polyacrylonitrile. Here again, it has beenfound practically impossible to obtain filamentary structures such asyarns from the composition. Films or filaments, when obtainable, areextremely brittle: they are highly colored a and very weak, presumablybecause of the presence within them of residual quaternary ammoniumsalt. Removal of this salt is diflicult and g polymer and which may besubstantially completely removed from the structures i'ormedof such asolution. g

It is another object of this invention to produce av solution ofpolyacryonitrile or a copolymer or interpolymer of acrylonitrile inwhich at least 85% by weight of the polymer is acrylonitrile, in asolvent which does not react with or decompose the polymer, the solutionbeing suitable for, the formation of commercially useful, void freearticles of polyacrylonitrile, for example yarns which are suitable astextile yarns and film which are suitable as wrapping tissue. a

It is another object of this invention to produce a solution ofpolyacrylonitrile, or a copolymer or interpolymer off-acrylonitrile inwhich at least 85% by weight of the polymer is acrylonL trile, in avolatile organic solvent, which solution is stable over extended periodsof time and is eminently suited for use in the manufacture of shapedarticles such as yarns, films, tubes, straws,

Example Fifteen parts of polyacrylonitrile possessing an averagemolecular weight of 120,000 are ground to an average particle size of200 mesh and intimately mixed with 85 parts of malononitrile, themixture then being heated over a period of fifteen minutes to atemperature of 150 C. to form a clear solution. The resulting solutionis cast at a temperature of 170 C. on to a polished, metal surfaceheated to a temperature of 100 C. to form a thin, transparent film ofpolyacrylonitrile.

artificial horsehair, bristles and ribbons, or when highly concentrated,for use in the manufacture of molded articles.

g It is a still further object of this invention to produce shapedarticles and structures of polyacrylonitrile, or copolymers orinterpolymers of acrylonitrile in which at least- 85% by weight of thepolymer is acrylonitrile.

It is still another object of this invention to produce a shaped articleor structure of polyacrylonitrile, or copolymers or interpolymers ofacrylonitrile in which at least 8* by weight of the polymer isacrylonitrile, for example a yarn, film, tube, bristleor, the like whichis tough, flexible, tenacious and free from voids.

Other objects of the invention will appear hereinafter.

. The objectsiof the invention may be accomplished in general bydissolving polyacrylonitrile, or copolymers or interpolymers ofacrylonitrile in which at least 85% by weight of the polymer isacrylonitrile, in a compound taken from the following group:

GEN

B can Malcnouitrile B,CEN j rr-c-n s-csn Methylsncthiocyanats ca 1 H QH.

s-osn Oyanomethylena thiocyanate The following example in which parts,proportims and percentages are by weight illustrates an application ofthe principles of the invention.

- mer molecule at least 85% by weight of-acryloni The polyacrylonitrilefor use with the invention is preferably'prepared by the ammoniumpersulfate catalyzed polymerization of mono nr'eric' acrylonitriledissolved or emulsified in water. It can, however, be prepared by anyother suitable type of polymerization reaction such as, for example, theemulsion type reaction disclosed by U. S. Patent No. 2,160,054 to Baueret al. The polymer preferably possesses a molecular weight within therange of 15,000'to 250,000 or even higher, as calculated from viscositymeasurements by the Staudinger equation:

N Molecular weight C=concentration of the solution expressed the numberof moles of the monomer (calculated) per liter of solution. 1

The molecular weight of the polymer obtained is dependent on'suchfactors as the concentration of the monomer in the water, the amount andtype of catalyst present, the temperature of th reaction, etc. Forexample, polyacrylonitrile' having a molecular weight of approximately60,000 can be prepared as follows: To 94 pounds of distilled waterheated to 40 C. add 40 grams of ammonium persulfate catalyst and gramsof sodium bisulfite activator. Then add 16 pounds of acrylonitrileslowly with stirring over a period of two hours. The polyacrylonitrilehaving the above said molecular weight will precipitate from thesolution. Increasing or decreasing the amount of the catalyst, whilemaintaining the other conditions constant, decreases or increases themolecular weight of the polymer. J Acrylonitrile copolymers andinterpolymers containing at least by weight of acrylonitrile andlikewise preferably having a molecular weight of 15,000 to 250,000 orhigher can be prepared in a similar manner.

Although the invention is preferably applied to the preparation ofsolutions of polyacrylonitrile, itcomprehends the dissolving ofcopolymers and interpolymers in polymerized or interpolymerized withother polymerizable substances such as, for example, com poundscontaining one or more ethylenic 1inkages including vinyl and acryliccompounds such as vinyl acetate, vinyl chloride, acrylic acid and itsesters and homologues as well as olefinic or dioleflnic hydrocarbonssuch as styrene, isobutylene and butadiene and polymers of suchsubstances. The solvents of this invention are eminently satisfactoryfor use with those polymers which contain a large amount ofacrylonitrile, forexample polymers that contain in the polywhichacrylonitrile is coaeoarar trile and which have generally been regardedby the art as being completely insoluble in all common organic solvents.Nor are these solvents limited to use with acrylonitrile polymers of anygiven molecular weight although they are especially satisfactory for usewith those polymers having an average molecular weight within the range15,000 to 250,000 as determined by viscosity data using the Staudingerequation and intended for use in the manufacture of yarns or film.

Acrylonitrilc polymer solutions formed by the" use of solvents embracedby the formulas set forth above are stable at room temperature(approximately 20 C.) and at temperatures considerably above roomtemperature. Shaped structures and articles can be produced by extrudingsuch solutions into an evaporative or coagulative medium.

The solutions are prepared by dissolving the polyacrylonitrile, orcopolymer or interpolymer of acrylonitrile with one or a mixture of theabove-mentioned solvents. These solvents dissolve or retain the polymerin clear solution only at elevated temperatures, for example attemperatures of 100 C. or higher, below which tem- Derature thecomposition resembles a gel. While at such elevated temperatures, thecomposition has the appearance of a'true solution, when cooled, itgenerally takes on the appearance of a gel which may, on standing,undergo syneresis. Reheating of this gel or syneresed mass howevercauses it to again return to solution form.

Shaped articles obtained from solvent solutions of polyacrylonitrile inaccordance with this invention and from which the solvent issubsequently removed are substantially free of foreign matter and voidsand substantially undecomposed and chemically unchanged from the polymerprior to its solution.

The above-described organic solvent solutions of acrylonitrile polymermay be shaped in the form of filaments, yarns, films, tubes and likestructures by apparatus and processes generally known in the art, thedetailed operating conditions being suitably modified.

Thus, the solution of the example can be extruded through a spinneretinto an evaporative atmosphere maintained at a temperature surficientlyhigh to substantially remove the solvent and, if desired, the bundle offilaments of yarn so coagulated by removal of the solvent can besubjected to a stretching operation as by passage at an elevatedtemperature between two draw rollers rotating at different rates oflinear speed, to orient the micelles of the filaments and therebyincrease tenacity as is described in the copending application of DanielT. Meloon, Serial No. 496,397, filed July 28, 1943. The evaporativemedium used in such a process may beany vapor inert to the solution suchas air, nitrogen, steam, etc., or any suitable mixture thereof andalthough the temperature of the evaporative medium is dependent on suchfactors as the dimensions of the spinning cell,.the composition and rateof extrusion of the spinning solution and the rate of flow of theevaporative medium, it is only nectraction of said-solvent; coagulatethapolymer in the spinning solution.-. suchlcoagulativ'e me-. dium whichwill be a chemicallyinertnomsolventfor the polymer may compriselwater,organic solvents such as alcohol, ethenetc or.

aqueous solutions of salts, alkalies or acids and in this wet spinningtype of process the stretching and. the subsequent orientation of thefilaments to improve tenacity, resilience, etc., is preferably performedwhile the article is in the gel State. e. g. while it still contains asubstantial amount of the coagulating bath liquid, the stretching takingplace by preference while the coagulating bath is maintained at anelevated temperature, e. g. C. ormore. The copending application ofWilliam W. Watkins Serial No. 496,376, filed July 28, 1943, covers theuse of glycerol and aqueous solutions of salts as baths, preferably atelevated temperatures, for the wet spinning of acrylonitrile polymeryarn, from solutions of the polymenpreferably withsubstantial tensionand stretch being applied during spinning.

As illustrated in the example, the solution may be cast in the form of afilm by passage from a hopper on to a metallic surface such as anendless steel band under the smoothing action or a doctor knife, thesolvent being removed either by the dry or evaporative method, or by thewet method utilizing a liquid coagulating bath, Solutions may also beused for the manufacture of molded articles or as lacquers or coatingcompositions, being especially useful in the coating, of wire and eletrical parts where high chemical and electrical resistance of thecoating is important.

The solution of acrylonitrilepolymer dissolved in an organic solvent inaccordance with this invention must be of such a concentration that itsviscosity at the operating temperature is within a workable range. Whenit is to be employed in the spinning of yarn or the casting of film, thesolution should preferably have a viscosity within the range of 25 to750 poises. When the polymer has a molecular weight of 250,000 or more,this requires that the maximum concentration of polymer in the spinningsolution be of the order of 10%. Generally, it is preferred that thespinning solution contain at least 10% of the polymer because of thedifllculty of rapidly removing large amounts of solvent from thesolution in the spinning operation. Moreover, it is conomicallyundesirable to use such large amounts of solvent for the spinning of agiven amount of polymer although it is true that the solvent can becompletely recovered from the spinning operation and reused. For thesereasons, it is preferred to employ a polymer having an average molecularweight of between 40,000 and 150,000 since such a polymer forms asolution of the desired viscosity in concentrations of the order of 15%to 25% and at a desirable spinning temperature of the order of 100 to C.Of course, it is within the scope of the invention to heat the solutionto a higher temperature, even to above the normal boiling point of thesolvent, for the actual spinning operation. Here again, the controllingfactor with regard to the temperature of the spinning solution is theviscosity of the solution.

In addition to acting as solvents, the compounds of this invention canalso be used as plasticizing agents for the polymer, when present insmall amounts. Non-solvent softeners such as glycerin can also beincorporated in the solutions of this invention to impart a softeningeffect to the subsequently formed articles.

especially useful for a variety of 7 This invention is primarilconcerned with the steps of dissolving polyacrylonitrile in a suitablesolvents do not cause a decomposition or chemical alteration of thedissolved acrylonitrile polymer.

At the same time, it is also characteristic that the solvents providedby the invention are also useful in the dissolving of mixturesofpolyacrylonitrile and adjuvants such as dye modifiers, linear polyamidessuch as nylon, derivatives of cellulose including cellulose ethers andesters, polymers of vinyl compounds such as vinyl chloride, vinylacetate, acrylic acid, etc., which adjuvants may be incorporated in theacrylonitrile polymer solution to modify the properties, both chemicaland physical, of the resulting shaped articles.

This invention provides a class of solvents for polyacrylonitrile, andcopolymers and interpolymers of acrylonitrile which were heretoforeconsidered substantially insoluble. The solvents are capable of formingwith the polymer clear solu-' tion that are stable for extended periodsof time at both room and elevated temperatures and are admirably suitedfor use as lacquers or coating compositions or in the manufacture ofshaped articles of the polymer, for example by extrusion into anevaporative or coagulative medium, or by the use of a molding technique.The solvents of the present invention are miscible with acrylonitrilepolymers containing at least 85% by weight of acrylonitrile in thepolymer molecule over a wide range of proportions and are particularlyuseful in forming solution containing or more by weight of the polymer.

The practice of the present invention makes possible the production,from polymers of acrylonitrile contemplated herein, of articles having awide range of utility because of the excellent physical and chemicalcharacteristics of the polymers. Thus, yarns composed of these polymersare not brittle, but are strong, resilient and possess good elongationand elastic recovery. Their specific gravity is low, being about 1.15 ascompared with 1.5 for cellulosic materials. Water absorption is very lowso that moisture causes no appreciable change in dimensions. When theyarn is wetted, it dries very quickly and does not shrink upon drying.The yarns are not affected by customary organic solvents, nor byoxidizing agents or acids except in extremely high concentrations.Sunlight or ultra-violet light ha little or no' effect upon it andinsects or micro-organisms do not attack it. The yarns exhibit a highmodulus and high impact strength.

Because of these properties, yarn composed of these polymers areespecially adapted for use as sewing thread, particularly whereresistance to chemicals, moisture, bacteria, mildew, acids, etc., isdesired. The yarns may be made into cords suitable for use in parachuteshrouds and webbing. cordage for use in the electroplating industry andfor conversion into ropes which can be used for halyards, climbingropes, glider tow ropes, landing nets, fishing nets or nets for sportslike tennis, badminton or the like. The yarns may be woven or knittedinto fabrics of all kinds.

purposes including fabrics for window shades, window curtains, balloonfabrics, parachute cloth, deck cloth for boats, airplane fabrics, canoecovers, sleeping bags, hunting coats, life-preserver covers, war mapfabrics and bolting or screening cloth. Be-

, 8,. cause of its dimensional stability and dye resist-' ance, fabricsfor use in screen printing may be made advantageously. Heavy fabrics foruse in the fabrication of jungle boots, jungle hammocks. automobiletops, harvester aprons, mine blankets, conveyor belts, especially whereresistance to acids, insects, mildew and bacteria is desirable, fabricsuseful in underground mining work, for

example in tubing for conveying air and other,

gases where high resistance to acid waters i required. Fabrics composedof these yarns find use in the manufacture of fire hose because of theirstrength and resistance to abrasion. Since the yarns exhibit highresistance to stain and are unture, high dielectric properties affectedby ultra-violet light, they are especially useful as table linens,aprons and the like where stainproofness is desirable and for use aszipper tapes, Venetian blind tapes, draperies and the like whereultra-violet resistance is important. Fab rics formed from these yarnsand, if desired. calendered and/or treated with a water repellant agenthave a special utility in raincoats and shower curtains, or if the weaveis made coarser, mosquito netting. Since the acrylonitrile polymerscontemplated by the invention are, among other things, highly resistantto chemicals other than alkalies, they can .be used as mechanicalpackings, particularly in the form of multifilament tow or rope which habeen braided into a structure of the kind customarily used for packingjoints surrounding moving shafts. Diaphragm fabrics for fuel pumps canalso be composed of the acrylonitrile polymers described herein.

Fabrics made from these yarns are extremely useful in the fabricationoflaminated structures. Excellent adhesive bond are obtained between theseacrylonitrile polymers and various resins, synthetic rubber and naturalrubber. Fabrics of these yarns impregnated with urea-formaldehyde,phenol-formaldehyde, melamine-formaldehyde resin and the like may beformed into laminated structures which have extraordinary properties ofdimensional stability, resistance to moisand the like which make themuseful for electrical insulating purposes, instrument panels, part forelectrical devices or mechanical equipment and the like. Panels forstructural purposes, wall board, side wall materials and bottommaterials for small boats, pontoons and containers of various kinds canbe made from these laminated materials.

Similarly, molded structures can be made by mixing staple or cut flockprepared from these acrylonitrile polymers with suitable bonding resinsof the urea-formaldehyde type which can be molded by extrusion orpressure. Cable conduits, tubing, piping and numerous other structurescan be made. P

Reference throughout the specification and claims .to acrylonitrilepolymers, polymers of 'acrylonitrile, and copolymers and interpolymersof acrylonitrile containing at least by weight of acrylonitrile"signifies polymers containing in their molecules at least 85% by weightof the acrylonitrile unit which is considered to be present in thepolymer molecule as the group Hr-JJH-CN that is, at least 85% by weightof the reactant material converted into, and forming the polymer isacrylonitrile.

Since it is obvious thatmany changes and modifications can be made inthe above described details without departing from the nature 9 andspirit of the invention, it is to be understood that the invention isnot to be limited to the details described herein except as set forth inthe appended claims.

I claim:

1. A new composition of matter comprising a polymer of acrylonitrilecontaining in the polymer molecule at least 85% by weight 01acrylonitrile and a compound taken from the class consisting ofmalononitrile, methylene thiocyanate and cyanomethylene thiocyanate.

2. As a new composition of matter, a polymer of acrylonitrile containingin the polymer molecule at least 85% by weight of acrylonitriledissolved in a compound taken from the class consisting ofmalononitrlle, methylene thiocyanate and cyanomethylene thiocyanate.

3. As a new composition of matter, polyaciylonitrile dissolved in acompound taken from the class consisting of malononitrile, methylenethiocyanate and cyanomethylene thiocyanate.

4. The composition of claim 2 characterized in that the polymer has amolecular weight of between 15,000 and 250,000.

5. The composition of claim 2 characterized in that the polymer has amolecular weight of between 40,000 and 150,000.

6. The composition of claim 2 characterized in that the solutioncontains at least 10% of the polymer.

7. The composition of claim 2 characterized in that the solution has aviscosity within the range of 25 to 750 poises.

8. The composition of claim 2 characterized in that the polymer ofacrylonitrile is polyacrylonitrile having a molecular weight of between15,000 and 250,000.

9. The composition of claim 2 characterized in that the polymer ofacrylonitrile is polyacrylonitrile having a molecular weight of between40,000 and 150,000.

RAY CLYDE HOUTZ.

